JP3247751B2 - An imaging device that aligns the image in the lateral direction of the photosensitive belt - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the alignment of a plurality of image exposures formed on a photoreceptor belt, and more particularly, to a belt that moves in a longitudinal direction but tends to be shifted laterally from a linear movement path. In the horizontal alignment of an image formed by exposure by horizontal line scanning.

2. Description of the Related Art In digital methods of producing color images by electrophotographic techniques, for example, each image area on a photoreceptor belt is subjected to at least four lateral line scans with a modulated laser beam or a linear array of light emitting diodes. Times, within a circle of 0.1 mm, ie ± 0.05
Must be aligned to a tolerance of mm. The longitudinal alignment of the image area within this range of accuracy, i.e. the belt, by providing timing marks on the belt in a longitudinal direction corresponding to the image area in combination with available electronic sensors and corresponding circuits Can be aligned in the moving direction. Aligning pixels or "pixels" laterally, i.e., in a direction orthogonal to the direction of belt travel, can be a combination of belt width manufacturing tolerances, support roller placement, non-uniform belt elongation, or a combination of these tolerances. Was more difficult by

Conventionally, the problem with the lateral alignment of pixels in multiple image exposures on a photosensitive belt is whether the belt is to be guided so that lateral displacement can be eliminated or at least reduced. It has been addressed by manipulating the belt in response to the detection of a lateral deviation from a true linear travel line. The most commonly used belt operating technique is to detect a lateral displacement of the belt by a belt edge sensor and control a mechanical operating mechanism so that it can be returned to an accurate movement line. there were. Such belt operating devices tend to be inaccurate due to belt width tolerances and edge undulations, and require mechanical operating mechanisms that require significant belt travel and time before belt displacement can be sensed electrically. I need.

An improved belt handling technique is described in co-pending application Ser. No. 07 / 635,835, filed Jan. 3, 1991, assigned to the same assignee as the present invention. This application discloses a lateral belt alignment mechanism for detecting a target pattern formed as an opening of a photosensitive belt at a position preceding each image exposure frame, the disclosure of which is included in the present description as a reference. . In that application, the target takes various patterns. In general, at least one reference target line and one target line inclined with respect to the belt moving direction are formed on the belt, and the target is spatially formed. The length of time during which these target lines pass through the fixed sensing axis varies with the lateral displacement of the belt. One example of a target pattern is shown in FIG. 5 of the pending application,
It forms a "Z" shape consisting of two lateral slots and one inclined slot. It has been found that this embodiment produces a satisfactory output signal from the corresponding sensor, allowing more precise control of the imaging optics.

However, a practical problem with the "Z" pattern is that the lateral slots formed by cutting slots at the inside or outside edges of the belt are such that they are not driven by photoreceptor drive rollers, drive units. When driven around the edge or around the idler rollers, they tend to wrap upward due to the stresses generated on them. The slot edge perpendicular to the belt movement (processing) direction is likely to wind upward. By winding upward, it projects above the belt surface, and may be caught and damaged by a sensor normally arranged close to the belt surface. The wrapped edge appears "wavy" to the sensor, causing a depth of field error. As a further problem, the "Z" pattern is prone to tearing and tearing due to periodic bending stresses and concentrations at the corners of the lateral slots.

Accordingly, it is an object of the present invention to improve alignment sensing when using a "Z" shaped pattern. When all three slots are inclined by a predetermined angle with respect to the horizontal line, and a Z-shaped pattern of "italic" in which none of the edges are orthogonal to the moving direction of the belt is formed on the belt surface, It has been found that stress related problems are greatly reduced and the wrapping phenomenon is eliminated. That is, the present invention is exposed in an imaging apparatus that form a large number of image exposure frames on a photoconductive member, it is possible to form an integral image exposure frame, a plurality of target openings respectively corresponding to the exposure frame A photoreceptor belt provided outside the region, and detection means provided corresponding to the target opening, for detecting a change in a lateral position of each opening when the opening provided in the belt moves in a processing direction. When, by a means for generating a signal for adjusting the lateral position of the exposure frame corresponding to the detected lateral position of the opening
The opening has three sets of slanted slots, each slot having 0 with respect to a horizontal line orthogonal to the processing direction.
Alternating inclines of angle .theta. In excess of degrees are alternated, and each slot is for an imaging device that is separated from each other by a distance S in the processing direction when the belt is in the proper alignment position.

FIG. 1 is a schematic perspective view of an apparatus incorporating the present invention for performing multiple exposures on a photosensitive belt by passing the image area on the photosensitive belt multiple times through a single raster output scanner. is there.

FIG. 2 shows a target pattern according to the present invention.

FIG. 3 illustrates a voltage waveform signal generated by the pattern shown in FIG. 2 and a method of converting the signal into a measure of lateral displacement.

FIG. 4 shows the stress acting on the target pattern of FIG. 2 in comparison with the stress acting on the conventional target pattern.

FIG. 1 shows a preferred embodiment of the present invention incorporated in a schematically illustrated multi-pass electrophotographic printing apparatus 10. The photosensitive belt of the apparatus 10 is hung on guide rollers 14 and 16 and at least one of them is driven to move the belt 12 in the direction of arrow 1.
8 in the longitudinal (processing) direction. Belt 1
2 is set to a length that can provide integer image areas I _{1 to In n} separated from each other and represented by a dotted rectangle in FIG. Each of the image area I ₁ ~I _n is dotted arrow 20
Upon reaching transverse scan line shown in, it is successively exposed on transverse raster lines 22 in the vicinity are shown exaggeratedly longitudinal spacing on the image area I ₁ of FIG.

In the embodiment of FIG. 1, the modulated laser beam 24
Is reflected by the continuous surface 25 of the rotating polygon mirror 26 onto the line 20 so that the line 20 is scanned by a ROS (raster output scanner). The beam 24 originates from a laser device 28 such as a laser diode operated by a laser drive module 30 forming part of a control processor 32. The processor 32 is provided with other circuits or logic modules described in FIG. 1, and is also provided with a scanner drive command circuit 34 for controlling the operation of a motor (not shown) for rotating the polygon mirror. .

In operation of the apparatus 10 described above, the processor 32 exposes each raster line 22 in response to a video signal to obtain a line segment of the video signal image. In an electrophotographic color device, each image area I ₁ to
The I _n once for each and black primary colors, respectively,
A total of four exposures must be made. Apparatus 1 in which only one raster output scanner or head is used
In a multi-pass apparatus such as 0, it is necessary to rotate the belt 12 four times to completely expose each image area. As is well known in the art, single-pass devices sequentially expose each image area with four raster output scanners, each equipped with a dedicated polygon mirror. Continuing with the description of FIG. 1, a result of the belt 12 moves in the longitudinal direction, since each raster line 22 is aligned with the transverse scan line 20, sequentially exposed on a raster line 22 on which the image area I ₁ ~I _n are consecutive Is done.

The horizontal scanning line 20 or the horizontal scanning line 20
The length of a to 20d is longer than the lateral dimension of the image area I. In that regard, the scan line length is determined by the length of each mirror surface 25 and exceeds the length of the raster line 22. The length of each raster line is determined by the time the laser diode is activated to reflect the modulated beam at each face 25 on the rotating polygon mirror 26 as determined by the laser drive module 30. Thus, control of the laser drive module 30, is displaced by the lateral position of the displaced exposed raster lines 22 and the image area I ₁ ~I _n against the belt 12, the active portion of each transverse scan line in the transverse direction be able to.

In accordance with the present invention, a signal is generated which indicates that the belt movement is out of line, thereby determining the exact lateral position of the first of the continuous image exposures relative to the photoreceptor belt. By adjusting the active portion of the transverse scan line 20 as needed, the continuous image is accurately longitudinally aligned or laterally aligned with the first image, regardless of the lateral position of the belt during image exposure. Can be aligned in any direction. This effect can be seen in the “Italic” targets T ₁ to T ₁ described in more detail with reference to FIGS.
This is made possible by providing T _n . These targets are arranged in alignment in the longitudinal direction along the edge portion of the belt 12, slightly forward position of each image area I ₁ ~I _n, i.e. arranged upstream of the image area in the direction of belt travel Have been. Single sensor 36 is arranged to match the target T ₁ through T _n.

As shown in FIG. 1, the sensor 36 has a bifurcated or horseshoe shape and includes upper and lower legs 38 and 4.
0, so as not to obstruct the longitudinal movement of the belt surrounds the edges of the belt 12 provided with a target T ₁ through T _n. While a light source such as a light emitting diode 42 is supported on the upper leg 38, a light detector such as a photodiode 44 is supported on the lower leg 40, which is generally detected by a photodiode. Included in a circuit (not shown) that generates a voltage signal in response to the light. The light emitting diode and the light detecting diode are aligned on a common optical sensing axis.

FIG. 2 is an enlarged view of one of the targets T ₁ of FIG. The target is formed by three open slots 50, 52, 54 cut into the belt 12 or otherwise formed. Each opening is
It is formed at an angle θ with respect to a line perpendicular to the moving direction. Preferably, the ends of each slot are rounded. As described above, the third inclined slot 52 is disposed between the leading slot 50 and the final inclined slot 54 inclined at the angle θ. Light from the light emitting diode 42 in the sensor 36 is blocked at the leading edges of the three slots. The point at which each slot is detected and sensed by the photodiode 44 is converted into information defining a lateral direction. When the belt 12 is in the center position, the sensing axis uses the line L as a target. The distance between the detection points between the slots 50 and 52 and between the slots 52 and 54 is S. For example,
When the belt is displaced leftward with respect to the center position L, a new line M is formed in the moving direction. Of course, the belt may be displaced to the right or to another position in between.
For example, if the belt is displaced to the left by a distance X, the leading edge of each slot will be detected along the axis M to the right.

In this case, the distance between the detection points changes.
That is, S ₁ is a distance obtained by adding the distances Y ₁ and Y ₂ to the initial distance S, whereas S ₂ is a distance obtained by subtracting the distances Y ₂ and Y ₃ from the initial distance S. The distances Y ₁ , Y ₂ and Y ₃ are of the formula: Y ₁ = Xtan (θ); Y ₂ = Xtan (θ); Y ₃
= Xtan (θ). It can be seen that the distance X is determined by the following equation: X = (S ₁ −S ₂ ) / (4 tan θ) (1) where S ₁ = S + Y ₁ + Y ₂ , that is, S ₁ = S + 2X tan (θ) (2) S ₂ = S−Y ₂ −Y ₃ , that is, S ₂ = S−2Xtan (θ) (3)

FIG. 3 shows the photodiode 4 of the sensor 36.
4 shows the two voltage signals after level sensing and squaring generated from FIG. The two signals V _L and V _M correspond to the voltage signals generated by the photodiode 44 when the target T is at a position corresponding to the respective trace lines L and M. Utilizing these voltage signals, the encoder clock pulse counter 58, shown schematically in FIG. 3, can be controlled by a series of parallel lines representing clock pulse increments. In fact, counter 58 is included as a component of control processor 32 (FIG. 1).

In FIG. 3, if the center of the target T is located on the optical sensing axis common to the diodes 42 and 44 of the sensor 36, the sensing axis is located on the trace line L while the target T moves past the sensor. are doing. As each slot 50, 52, 54 passes through the sensing axis, the photodiode 44 generates an output waveform signal, the spacing of the waveform being a value correlated with the separation S between each slot. When the sensing axis is displaced to the right by a distance X to the M axis (the belt is moved to the left), the output voltage generated by the sensor is separated by a time length corresponding to the distances Y ₁ , Y ₂ and Y _3. . The output signal is processed in a timing / calculation circuit 60 that performs a mathematical operation to solve Equation 1 for X. Counter 58 generates clock pulses having the following relationship for slots 50, 52 and 54: The first encoder pulse number n ₁ is gated by the leading edges of slots 50, 52. The second encoder pulse number n ₂ is
Gated by the leading edges of slots 52 and 54. If the encoder resolution C is equal to the belt speed divided by the encoder frequency (mm / pulse), the following relationship exists: n ₁ · C = S ₁ = S + 2X tan (θ) n ₂ · C = S ₂ = S−2X tan (θ) After solving Equation 1 for X, the correction voltage is fed to the laser drive unit 30 (FIG. 1) in a feedback loop. To adjust the start of the scan and provide proper alignment to the new lateral position of the belt.

FIG. 4A is an explanatory view of the stress applied when the italic Z-shaped target of the present invention passes around the photoreceptor belt rollers 14 and 16. Since each slot is inclined, the stress at the corner of the slot is θ =
When it is 45 °, it is reduced by a factor of two. FIG. 4B shows that the slots are provided in a direction orthogonal to the processing direction.
It can be seen that the stress is considerably reduced as compared with the prior art.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an apparatus incorporating the present invention for performing multiple exposures on a photosensitive belt by passing an image area on the photosensitive belt multiple times through a single raster output scanner.

FIG. 2 shows a target pattern according to the present invention.

3 shows a voltage waveform signal generated by the pattern shown in FIG. 2 and a method of converting said signal into a measured value of lateral displacement.

FIG. 4 shows the stress acting on the target pattern of FIG. 2 in comparison with the stress acting on a conventional target pattern.

[Explanation of symbols]

12 photosensitive belt, 42 light emitting diode, 44 photodiode, 50, 52, 54 slot, 58 encoder clock pulse counter, T target aperture

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-173612 (JP, A) JP-A-3-252691 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/44-2/455 B41J 2/525 B41J 13/00 G03G 15/01 G03G 21/00 H04N 1/46 G01M 11/00

Claims (3)

(57) [Claims] 1. A imaging apparatus that form a large number of image exposure frames on a photoconductive member, it is possible to form an integer of image exposure frames, exposing a plurality of target opening corresponding to the respective exposure frame area A photoreceptor belt provided on the outside, and provided corresponding to the target opening,
Detecting means for detecting a change in the lateral position of each opening when the opening provided in the belt moves in the processing direction; and adjusting the lateral position of the exposure frame in accordance with the detected lateral position of the opening. and means for generating a signal to open <br/> port has a in each of the three sets of inclined slots, more than 0 degrees with respect to the horizontal line in each slot perpendicular to the process direction An imaging device wherein the slopes of the angle [theta] are alternately different and each slot is separated from each other by a distance S in the processing direction when the belt is in the proper alignment position. 2. The laterally displaced distance X of the belt is defined as X = (S ₁ −S ₂ ) / (4 tan θ) where S ₁ = S + 2X tan (θ) and S ₂ = S−2X tan (θ) . The imaging device according to claim 1, wherein 3. An encoder controlled by said detecting means.
The Dachlock pulse counter is the first two ramp slots.
The first number of pulses n ₁ and the maximum
A second representing the increment between detecting the last two inclined slots
Where n ₁ is the number of pulses n ₁ · C = S ₁ = S + 2X tan (θ) n ₂ · C = S ₂ = S-2X tan (θ) where C is the resolution of the encoder clock pulse counter
3. The imaging device according to claim 2, wherein